<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var arr = [
            [12,4,324,61],
            [1,21,4],
            [66,3,54,34]
        ]
        console.log(arr[1][1])

        /**
         * 使用二重循环
         */

    </script>
</head>
<body>

</body>
</html>